The present invention relates to a device for supplying fuel and comburent agent to at least two arrays of burners, in which each burner is connected to a fuel inlet line and to a comburent agent inlet line and these lines are connected by means of a corresponding manifold respectively to a fuel supply duct and to a comurent agent supply duct A device for this kind is known from the documents U.S. Pat. No. 4,043,742, 4,825,353A. 4,834,644A 3,760,775 a.
The function of the burners in heating furnaces is to raise a charge from a lower temperature at which it enters the furnace to a higher temperature at which it leaves the furnace, in order, for example, to heat and raise the temperature of a slab which is to be rolled on leaving the furnace. The charge is heated, as is known, by the transmission of the heat generated by the combustion products by processes of radiation and convection. Before its removal from the furnace, the charge is held in areas of the furnace having a lower temperature. The purpose is to keep the mean temperature reached during heating constant, thus keeping the non-uniformities of heating within tolerances acceptable for the final rolling. These areas are known as equalizing or soaking areas.
In these equalizing areas, in which the power required is lower than the maximum power, the operation of the burners of the array can be controlled by making each burner operate at a mean power of, for example, 30-40% of the maximum power, and therefore below the optimal operating range, or by igniting one or more burners of the array or arrays in rotation with an individual load as close as possible to the maximum.
The object of the present invention is to provide a device for supplying one or more arrays of burners which, if it is necessary to control the power to be supplied to the burners, makes it possible to predetermine, upstream of the array or arrays, the flows of fuel and comburent agent required for these burners, according to a specific fixed ratio of fuel to comburent agent and according to the power required by the furnace at a specific moment, thus making it unnecessary to control each individual burner.
This object is achieved by the present invention by means of a device according to the pre-characterizing part of the claim and characterized by the combination of the following features:
a) in the proximity of each burner in the corresponding fuel inlet line is provided a valve for shutting off the flow of fuel to the burner and in the corresponding comburent agent inlet line is provided a valve for shutting off the flow of comburent agent to the burner,
b) in the fuel supply duct is provided a control valve for controlling the flow of fuel and upstream of this control valve is provided a device for measuring the flow of fuel,
c) in the comburent agent supply duct is provided a control valve for controlling the flow of comburent agent and upstream of this control valve is provided a device for measuring the flow of comburent agent,
d) the devices for measuring the flows of fuel and of comburent agent and the control valves are operatively connected to a programmable logic unit, which receives at its inputs the data from the devices for measuring the flow of fuel and the flow of comburent agent and the data relating to the power required by the arrays of burners, as well as the data relating to a predetermined value of the ratio between fuel and comburent agent, and supplies at its outputs signals for controlling the opening of the control valves in order to keep the ratio between the flow of fuel and the flow of comburent agent to the predetermined value,
during the operation the valve provided in the fuel inlet line and the valve provided in the comburent agent inlet line corresponding to a part of the burners of each array of burners are closed, thus rendering inactive the respective part of burners.
By means of the present device, therefore, it is possible to allow the burners to operate, regardless of the power required for treating or heating a charge, in areas close to those of their optimal operation, and it is also possible, for situations in which the required power is less than the maximum, to make one or more burners of a specific array operate in rotation.